1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for implementing an assisted cross-protocol adaptation layer (cross-PAL)/cross-layer clock synchronization scheme for WiGig communications in WiGig 60 GHz mmWave wireless communication systems.
2. Related Art
The next step in wireless communication is nearing. A first generation of mmWave, such as 60 GHz, wireless communication systems is in the process of being standardized as, for example, the proposed IEEE 802.11ad/WiGig standard. A broad spectrum of products that support mmWave wireless communication are being developed and manufactured.
The Wireless Gigabit Alliance (WiGig) has defined the specification for the 60 GHz MAC and PHY layers. The WiGig MAC/PHY specification enables data rates up to 7 Gbps, which is significantly faster than any data rate available in Wi-Fi networks based on current standards. WiGig systems operate in the 60 GHz frequency band, and have a broader spectrum available than the 2.4 GHz and 5 GHz bands used by existing Wi-Fi communications. This allows wider bandwidths that support faster transmission speeds.
WiGig has defined multiple protocol adaptation layers (PALs) directly on top of the 60 GHz MAC and PHY layers. This is not a wholly new concept in that other standards, such as Wi-Fi, define similar or different protocol adaptation layers that facilitate specific applications over different MAC and PHY layers. FIG. 1 illustrates an example of the currently proposed WiGig layering model. As shown in FIG. 1, multiple PALs 120-150 are specified directly on top of the WiGig 60 GHz MAC layer 110 and the WiGig 60 GHz PHY layer 100. These separate PALs 120-150 provide for optimal support of different types of applications according to the WiGig proposed standards for 60 GHz wireless communication. For example, the recently-developed WiGig Display Extension (WDE) PAL 120 supports wireless transmission of audio/video data via multiple interfaces and offers key audio/video applications, such as transmission of compressed or uncompressed video from a computer or digital camera to an HDTV, a monitor or a projector. The WiGig Serial Extension (WSE) PAL 130 defines high-performance wireless implementations of widely-used computer interfaces over 60 GHz enabling the multi-gigabit wireless connectivity between devices for, for example, USB type data traffic. The WiGig Bus Extension (WBE) PAL 140 supports Peripheral Component Interconnect Express (PCIe) data traffic. A separate Secure Digital Input/Output (SDIO) PAL 150 supports SDIO traffic. Additionally, the WiGig architecture and standards leave open the possibility that other PALs may be specified to support other traffic types as may be defined by WiGig in the future.
In the currently-proposed WiGig systems, there may be multiple PAL layers operating over the WiGig MAC and PHY layers as shown in FIG. 1. Most of the applications running in these WiGig PALs require a level of synchronization between the WiGig PAL transmitter (source device) and the WiGig PAL receiver (sink device) for the individual PALs. Clock synchronization is a process in which a receiver's clock is set to correspond to, and remain the same as, the transmitter's clock.
This synchronization is needed for different purposes in different WiGig PALs and in different WiGig layers in which the clocks may run at different frequencies. For example, in the WiGig 60 GHz MAC and PHY layers 100,110, clock synchronization is provided in an attempt to ensure that the received signals are sampled at a correct time in order to avoid any alias of the transmitted signal being received by the receiver.
In a WiGig WDE PAL, for example, the clock synchronization is required to attempt to ensure that data bits are removed from the WiGig WDE PAL receiver buffer at a same rate (speed) that the data bits are transmitted into the WiGig WDE PAL receiver buffer by the WiGig WDE PAL transmitter. Doing so avoids buffer underflow or overflow to a maximum extent possible in order to maintain fidelity of the data stream and to further attempt to ensure that what the WiGig WDE PAL receiver receives and delivers as an output is substantially identical to what the WiGig WDE PAL transmitter transmitted.
Clock synchronization mechanisms are defined separately and independently for different PALs/layers and the tasks that are carried out by each PAL or PAL related radio on their own.
The process of separate independent clock synchronization for each individual WiGig PAL tends to be laborious and time consuming. The process includes a series, and potentially a large series, of individual time stamps being sent from the transmitter (source) side to the receiver (sink) side with the transmitter and the receiver in a master-slave relationship. The receiver attempts to synchronize its clock to the clock in the transmitter based on the time stamps sent from the transmitter. The time stamps are individual data frames defining a current time for the transmitter. The receiver compares the receiver's time with the transmitted time stamps and makes a correction in slowing down or speeding up the receiver's clock.
In a beginning of the clock synchronization process, the receiver must search for synchronization with the transmitter. In these instances, significantly high numbers of time stamps may be required to confirm synchronization of the receiver's clock with the transmitter's clock. There is a series of comparison and adjustment steps undertaken by the receiver to ultimately confirm clock synchronization for an individual PAL by converging deviations from the time stamps in the receiver to the time stamps themselves.
Once an individual WiGig PAL is synchronized, the process of synchronization needs to be undertaken separately, and through a correspondingly lengthy process as described above, for each individual PAL.